EVALUATION OF CITRUS CULTIVARS/GERMPLASMS OF ASSAM AGAINST CITRUS CANKER DISEASE
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Date
2021
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AAU, Jorhat
Abstract
Evaluation of different citrus cultivars/germplasms against citrus canker disease in artificially inoculated conditions and their assessment for defense-related secondary metabolites, viz., total phenol, flavonoid, alkaloid content was attempted in the present study. For artificial inoculation, bacterial pathogen associated with diseased citrus canker leaf was isolated, purified, and further confirmed as Xanthomonas citri pv. citri by conducting morphological, cultural, gram staining, specific biochemical tests, and molecular characterization. Altogether thirty cultivars/ germplasms were tested for their degree of resistance against citrus canker (X citri pv. citri). All these cultivars/ germplasms showed significant differences in terms of percent disease severity and disease reaction. Out of thirty, eight cultivars/germplasms namely Jora tenga (14.67%), Bonjora (15.58%), Holong tenga (15.75%), Patijora (17.75%), Birajora (18.50%), Cleopatra mandarin (20.00%), Latipes (17.34%) and Ada jamir (20.18%) exhibited resistance response (R). Moderate degree of susceptibility (MS) was observed in fourteen cultivars/germplasms viz., Trifoliate orange (25.63%), Troyer citrange (26.87%), Rubidoux (30.37%), NRCC6 (36.58%), Bhutan orange (31.06%), Galgal
(38.42%), Sopai (39.70%), Rangpur lime (43.30%), Soh bitara (30.27%) Sohmyndong
(46.57%), Pummelo-1(31.34%), Pummelo-2 (28.38%), Pummelo-3(38.48%), Pummelo- 7(43.31%). Seven cultivars/germplasms namely Nainty jambhiri (52.56%), Australian orange (56.32%), Rough lemon (57.54%), Volkameriana (60.34%), White pummelo (61.64%), Acid lime (62.48%) and Grape fruit (70.63%) were categorized as susceptible types (S) while Assam lemon showed the highest degree of susceptibility (HS) against citrus cankerwith 78.14% disease severity. Further study on secondary metabolites revealed that total phenol, flavonoid, alkaloid content in citrus leaves differed greatly based on the cultivars/germplasms. The highest total phenol content (TPC) was found in one of the resistant germplasm Latipes (21.26 mg/g dry weight), while the lowest was recorded in susceptible cultivar Grapefruit (7.85 mg/g dry weight). Another resistant germplasm Jora tenga (6.47 mg/g dry weight) had the highest flavonoid content and the lowest was found in susceptible germplasm White pummelo (1.89 mg/g dry weight). Similarly, the highest alkaloid percentage was found in resistant germplasm Adajamir (10.52%) and the lowest was recorded in susceptible germplasm Volkameriana (2.30%). From the correlation analysis, three negative correlation coefficient was obtained viz.,P(rxy)= -0.861 for total phenol content, F(rxy)= -0.836 for flavonoid content and A(rxy)= -0.802 for alkaloid content.